1. Field of the Disclosure
The present disclosure relates to a method of fabricating a thin film transistor substrate and an organic light emitting display device using the thin film transistor substrate, and more particularly, to a method of fabricating a thin film transistor substrate and an organic light emitting display device using the thin film transistor substrate where a flexible display is obtained.
2. Discussion of the Related Art
Recently, multimedia devices, such as an organic light emitting display (OLED) device, a liquid crystal display (LCD) device, an electrophoretic display (EPD) device, a plasma display panel (PDP) device, a thin film transistor (TFT), a microprocessor and a random access memory (RAM), have been developed, and thus the importance of a flexible electric element has increased. Regarding the various display devices, it has been an interest of the industry whether a typical process of a thin film transistor (TFT) can be applied for an active matrix organic light emitting display (AMOLED) device having a highest possibility for a flexible display.
Specifically, properties, such as a thin profile, a light weight and an unbreakable property, are required for a mobile device, such as a digital camera, a video camera, a personal digital assistant (PDA) and a portable phone. Accordingly, a flat panel display (FPD) is fabricated by using a thin glass substrate. Alternatively, after a FPD is fabricated using a typical glass substrate, a thickness of the typical glass substrate is reduced through a mechanical method or a chemical method.
A typical glass substrate for a FPD has an advantage of stability in a process for forming an electrode or a TFT. However, since the typical glass substrate is hard and heavy, the typical glass substrate is not adequate for a flexible display as a display for mobile communication. Accordingly, a transparent and pliable plastic substrate has been suggested for a flexible display.
However, a plastic substrate is heat-resistant up to a relatively low range of about 150° C. to about 200° C. Since it is hard to perform a heat treatment for a transparent electrode formed on a plastic substrate through a sputtering method using indium-tin oxide (ITO), there exist several limitations on reduction of resistivity of the transparent electrode. In addition, since a thermal expansion coefficient of an ITO electrode is smaller as compared with that of a polymer plastic substrate, the ITO electrode and the plastic substrate expand with different rates from each other due to long heat history during a fabrication process or during an operation of a FPD. As a result, the plastic substrate is deformed. In a fabrication process of a low temperature polycrystalline silicon (LTPS), specifically, since a temperature of a substrate increases up to a range of about 400° C. to about 500° C., it is hard to adopt a plastic substrate.
In addition, since a plastic substrate has a relatively low strength, the plastic substrate is easy to be broken or cracked. Further, the plastic substrate may be warped and a resistance of an electrode on the plastic substrate may increase.
For the purpose of solving the above problems, a method using a carrier substrate has been suggested. After a separation layer is formed on a carrier substrate, such as a glass substrate, a plastic substrate is formed on the separation layer by coating a plastic material, and a thin film transistor array is formed on the plastics substrate. Next, the plastics substrate is separated from the carrier substrate.
However, the above method using a carrier substrate has a disadvantage of forming an additional separation layer. In addition, since a carrier substrate is hard to support a weight due to a property of a plastic substrate, it is hard to handle the plastic substrate.